0027974: Visualization, ray tracing - Improve ray tracing engine

* Multiple importance sampling for path tracing
* Improved light sources sampling (better handling several light sources)
* Fixed issues in light source intersection (light distance is taken into account)
* Add new TCL sample - OCCT Ball model for demonstrating physically-based materials
* Fix potential issue on NVIDIA GPUs ("Error: Failed to upload light source buffer")
* Path tracing materials reviewed; directional light source was smoother by default

samples/tcl/pathtrace_ball.tcl

@@ -0,0 +1,78 @@
+# Script demonstrating Global illumination materials
+# using path tracing rendering engine in 3D view
+
+#Category: Visualization
+#Title: Path tracing - Ball
+
+set aBallPath [locate_data_file occ/Ball.brep]
+
+pload MODELING VISUALIZATION
+
+# Setup 3D viewer
+vclear
+vinit name=View1 w=512 h=512
+vglinfo
+vvbo 0
+vsetdispmode 1
+
+# Setup view parameters
+vcamera -persp
+vviewparams -scale 18 -eye 44.49 -0.15 33.93 -at -14.20 -0.15 1.87 -up -0.48 0.00 0.88
+
+# Load the model from disk
+puts "Importing shape..."
+restore $aBallPath ball
+
+# Tessellate the model
+incmesh ball 0.01
+
+# Display the model and assign material
+vdisplay -noupdate ball
+vsetmaterial -noupdate ball glass
+
+# Create a sphere inside the model
+psphere s 8
+incmesh s 0.01
+vdisplay -noupdate s
+vsetlocation -noupdate s 0 0 13
+vsetmaterial -noupdate s plaster
+
+# Create chessboard-style floor
+box tile 10 10 0.1
+eval compound [lrepeat 144 tile] tiles
+explode tiles
+for {set i 0} {$i < 12} {incr i} {
+  for {set j 1} {$j <= 12} {incr j} {
+    ttranslate tiles_[expr 12 * $i + $j] [expr $i * 10 - 90] [expr $j * 10 - 70] -0.15
+    vdisplay -noupdate tiles_[expr 12 * $i + $j]
+
+    vsetmaterial -noupdate tiles_[expr 12 * $i + $j] plaster
+
+    if {($i + $j) % 2 == 0} {
+      vbsdf tiles_[expr 12 * $i + $j] -kd 0.85
+    } else {
+      vbsdf tiles_[expr 12 * $i + $j] -kd 0.45
+    }
+  }
+}
+
+# Configure light sources
+vlight del 1
+vlight change 0 head 0
+vlight change 0 direction -0.25 -1 -1
+vlight change 0 sm 0.3
+vlight change 0 int 10
+
+# Load environment map
+vtextureenv on 1
+
+puts "Trying path tracing mode..."
+vrenderparams -ray -gi -rayDepth 10
+
+# Start progressive refinement mode
+#vprogressive
+
+puts "Make several path tracing iterations to refine the picture, please wait..."
+vfps 100
+puts "Done. To improve the image further, or after view manipulations, give command:"
+puts "vfps \[nb_iteratons\]"